Gravity door hinges are well known in the art. Such hinges typically include a fixed cam cylinder member having an inclined cam surface on its upper end and a rotatably and vertically displaceable cam cylinder member including a complementary cam surface on its lower end. An axial rod is inserted through the cam cylinder members such that the two inclined cam surfaces abut each other in a complementary relationship. The rotational cam member is operatively connected to a door such that when the door is opened by pushing or pulling, the door is slightly raised as the upper cylinder member is rotated relative to the lower cylinder member and the angled cam surfaces are brought out of complementary aligned relationship. As a consequence, when the pushing or pulling force is relieved, gravity causes the upper cam surface to retreat to its original complementary orientation relative to the lower stable cam surface.
In order to achieve the desired cooperative relationship between the cam surfaces of the prior hinge structures while also promoting extended useful life without failure, it has been necessary to utilize finely machined and heat treated metallic cylinder elements which are tapped to accept and retain the connecting axial rod in a stable orientation. The use of such manufacturing processes gives rise to substantial complexity in the assembly process. In addition, over a period of prolonged use, heat treated metallic materials may be susceptible to deformation. In particular, the cam surfaces may become abraded thereby resulting in edge deformities reducing the smoothness of the opening and closing operation. Moreover, if the axial rod itself is damaged, then the ability to achieve aligned rotation may be hindered or lost.